Image sensors are semiconductor devices that convert an optical image into an electric signal. Image sensors may be classified into charge coupled device (CCD) image sensors and complementary metal oxide silicon (CMOS) image sensors (CIS).
A CMOS image sensor includes photodiodes and MOS transistors in unit pixels and implements an image by sequentially detecting electric signals of the unit pixels using a switching method.
As CMOS image sensors with mega pixels have been recently developed, the pixel size becomes relatively smaller. Due to the reduction in the pixel size, a focus length of a microlens is also reduced. Therefore, a metal interconnection of a peripheral logic circuit surrounding a pixel tends to be limited.